Puzzle for the electronics gurus out there... failure in near vacuum enviroment.

I'm engaged in a high altitude project incorporating an automatic
camera. In order to ensure that the potential cameras selected were
capable of operating in a near-vacuum, two were tested in a vacuum
chamber. One was a Kodak Ke60, and the other was a Samsung 80Ti.
Both had leads soldered to the shutter contacts, which were controlled
by solid state relays via a microcontroller. The 80Ti's only other
modification was removal of the large flash cap, as we were not
planning on using a flash (not that a flash at 100k ft would do any
good anyway). The 80Ti operated throughout the test, while the Ke60
failed at around 1 PSI. The standard "burned electronics smell" was
present after opening the chamber.

After opening the case to the Ke60 to determine what cause the Ke60
failure, it looks like there was heating near the flash circuitry.
Specifically, there is some discoloration near the contacts to a
silver, eliptical-shaped capacitor (looks wrapped) with "333KS" on the
side. Is this a pressure sensitive component? (the chamber went from
14.7 PSI to about .05 PSI in about a minute, so it was rapid
depressurization). The large flash cap was still good, so I don't
believe this was the point of failure.

Could it have been this 333KS component? If not, what potential
components may have failed due to decreased ambient pressure?

Thanks in advance for any advice!
Dave

 

Why not contact Kodak?
http://www.kodak.com/global/en/service/contactKodak/digitalCameras.jhtml

 

Oh, trust me, I've tried. They couldn't even give me a definative
low-temp operating condition. Apparently, the customer service group
(in America) is not associated with the engineering group... (Japan
maybe?)

 

Yeah, that's a possibility. But I don't believe any of the components
in the failure area depend highly on convection. In addition, it was
only after the 3rd shot that the camera failed, with 20 seconds of
time in between powering off and powering back up for a picture... I
don't think that's enough time or a high enough duty cycle for a
component to burn out...

 

---
If it's not that, then you may have lucked out ;^) and gotten a camera
with a bad component.

When you say the area around the "contacts" of the capacitor was
discolored do you mean where the cap's leads were soldered into the PCB?
If so, it could be that a high-resistance solder joint exists there and
is heating up, possibly aggravated by the inability of the heat
generated to be removed by convection. You may want to try either
touching it up (the joint) with a hot iron and a little extra solder or
solder-sucking it clean and re-soldering it. OTOH, the discoloration
may have been caused by arcing occurring because of a combination of
high voltage (the trigger pulse) and the low pressure allowing a cap to
discharge across the PCB.

 

Dave,

If you don't need the flash, why not just remove the components associated
with it and re-test?

I live in Rochester NY, home town of Kodak. Your experience with their
customer "help" is. unfortunately, typical of the company as a whole.
They are a company where filling dead shoes was the only way to gain
promotion and who really haven't moved with the times. But they, somehow,
still make damned good digital cameras!

John

 

re: >But they, somehow,

Starting when?

Don

 

Dave -

Something I have done in the past with great success (although not with
Kodak) is to bypass customer support and engineering and go right to public
relations. Tell them you are going to bad mouth them across the internet
with bad publicity if you don't get satisfaction. The last thing in the
world a smart company (and Kodak is that if nothing else) that spends
millions on advertising wants is widespread negative publicity. Let customer
relations do the leg work for you. That is what they get paid for.

 

When you removed all the air you removed the ability of the device to
cool itself, thus it overheated.

 

Again, as mentioned in a previous post, I don't believe that happened.
First, in a film camera, very few (if any) of the components depend
highly on convection (try to find a heat sink anywhere in a film
camera). In addition, it was only after the 3rd shot that the camera
failed, with 20 seconds of time in between powering off and powering
back up for a picture... I don't think that's enough time or a high
enough duty cycle for a component to burn out, based on the heat
capacity of even the small components. I've taken 36 shots in a 45
second period in normal conditions in a test to determine how quickly
it could take shots, and that'd tend to overheat any components much
more severly that 3 shots in a near vacuum.

Secondly, many other cameras are capable of operation in a vacuum, and
have been used in similar enviroments. It was obviously some thing or
some component specific to this design.

Dave

 

<snip>

How can low pressure increase the possibility of the cap discharging
across the PCB? I'm under the impression that the absence or presence
of air is almost negligible as far as any insulating conditions go...

Thanks,
Dave

 

<snip>

Yeah, I looked into that. Unfortunately, it looks like the flash
circuit is integrated closely into the other circuitry... in addition,
being an ME (and not an EE) doesn't help. I think I might just remove
the large flash cap and leave the oscillator circuit and the coil
intact. Could that potentially eleviate the problem?

Thanks,
Dave

 

It could cause other problems, though. for example, the charger circuit
senses the voltage on the cap and cuts off the oscillator when charging is
complete. If there is no cap, then it will either not run at all, which is
what you want, or run continuously, which is not desirable. The only way to
find out id to do it and see what happens..

If it runs continuously, you might try replacing the large cap with a small
ceramic, which would be impervious to changes in air pressure and wouldn't
hold enough charge to trigger the flash..

One thought; if the large cap is an electrolytic, and it is vented rather
than sealed, or if the sealing gave way, it would have dried out very
quickly under vacuum conditions. This may, repeat, may have caused your
problems.

Regards

John